The objectives of this study are: (1) to develop a stable technique for quantifying whole body acetate production in the young adult human; (2) to estimate in the young adult human the fraction of undigested sugar reaching the colon (i.e. lactulose) that is fermented to acetate and the proportion of acetate oxidized; and (3) to establish the variation in the 13C enrichment of plasma lactate during steady state after repeated oral doses of [1-13C]-acetate and apply these data to studies in premature infants.